Image transmission apparatus, image transport system and code amount control method

ABSTRACT

In order to enable efficient utilization of an available bandwidth by properly estimating the available bandwidth under conditions in which the available bandwidth significantly changes upon occurrence of communication path switching, an available bandwidth estimation is performed by estimating a current available bandwidth based on historical communication state information i.e. information on a past communication state stored in a storage to control a code amount used in encoding an image; upon occurrence of communication path switching (handover), acquiring a temporary available bandwidth value corresponding to a new (post-handover) communication path; generating new communication state information corresponding to a new communication state based on the temporary available bandwidth value; replacing the historical communication state information stored in the storage with the new communication state information; and estimating a new available bandwidth based on the new communication state information stored in the storage.

TECHNICAL FIELD

The present invention relates to an image transmission apparatus fortransmitting an image data to an image reception apparatus via acommunication path including a wireless section, an image transmissionsystem for transmitting an image data from an image transmissionapparatus to an image reception apparatus via a communication pathincluding a wireless section, and a code amount control method forcontrolling a code amount used in encoding an image to generate an imagedata and transmitting the image data to an image reception apparatus viaa communication path including a wireless section.

BACKGROUND ART

In recent years, various types of wireless communication methods havebeen widely used, and such types of wireless communication methodsinclude cellular communications such as LTE (Long Term Evolution) andwireless LANs, which allow a user to choose any of such wirelesscommunication methods as appropriate when performing wirelesscommunication.

There are existing techniques for providing proper control of datacommunication in a heterogeneous network; that is, a communicationenvironment in which different types of wireless communication methodsare mixedly used, and examples of such known techniques include acommunication method in which, upon receiving a notification of handovercompletion, a communication system recognizes a new communication pathused after the handover, predicts a frequency of occurrence of packetlosses in the new communication path, and then starts high speedwireless communication, and in which, when a new communication path hasa room of available bandwidth capacity, the communication system isallowed to encode data to be transmitted at a high-quality encoding rate(See Patent Document 1).

PRIOR ART DOCUMENT (S) Patent Document(s)

Patent Document 1: JP2012-049913A

SUMMARY OF THE INVENTION Task to be Accomplished by the Invention

Moreover, some studies in the field of mobile communication have beenfocusing on 5G systems (5th generation mobile communication system), andsuch 5G systems studies support, in addition to existing wirelesscommunication methods, cellular communication methods utilizing a highSHF (Super High Frequency) band or WiGig (Registered Trademark)communications utilizing millimeter bands, and other different wirelesscommunication methods. User of these technologies would advantageouslyexpand a range of users' choices of usable types of communication paths.However, in this case, there can be massive differences in availablebandwidths between different types of communication paths, resulting ina problem that an available bandwidth can significantly change when aswitch from a communication path to another (handover) occurs.

However, the above-described existing technologies cannot provide propercontrol of communication when an available bandwidth substantiallychanges, resulting in a significant decrease in the accuracy ofestimation of available bandwidth to be used. That is, an estimatedavailable bandwidth is greatly different from the actual availablebandwidth, which delays final determination of an estimated availablebandwidth, thereby inconveniently preventing effective utilization ofavailable bandwidths.

The present invention has been made in view of such problems of theprior art, and a primary object of the present invention is to providean image transmission apparatus, an image transmission system, and acode amount control method, which enables efficient utilization of anavailable bandwidth by properly estimating the available bandwidth evenwhen the available bandwidth significantly changes upon occurrence ofcommunication path switching.

Means to Accomplish the Task

An aspect of the present invention provides an image transmissionapparatus for transmitting an image data to an image reception apparatusvia a communication path including a wireless section, the imagetransmission apparatus comprising:

a communicator configured to transmit the image data to the imagereception apparatus;

a storage configured to store historical communication state informationwhich is information on a past communication state; and

a controller configured to estimate a current available bandwidth basedon the historical communication state information to control a codeamount used in encoding an image,

wherein, upon occurrence of communication path switching, the controlleracquires a temporary available bandwidth value corresponding to a newcommunication path, generates new communication state informationcorresponding to a new communication state based on the temporaryavailable bandwidth value, replaces the historical communication stateinformation stored in the storage with the new communication stateinformation, and estimates a new available bandwidth based on the newcommunication state information stored in the storage.

Another aspect of the present invention provides an image transmissionsystem for transmitting an image data from an image transmissionapparatus to an image reception apparatus via a communication pathincluding a wireless section,

wherein the image transmission apparatus comprises:

a communicator configured to transmit the image data to the imagereception apparatus;

a storage configured to store historical communication state informationwhich is information on a past communication state; and

a controller configured to estimate a current available bandwidth basedon the historical communication state information to control a codeamount used in encoding an image;

wherein, upon occurrence of communication path switching, the controlleracquires a temporary available bandwidth value corresponding to a newcommunication path, generates new communication state informationcorresponding to a new communication state based on the temporaryavailable bandwidth value, replaces the historical communication stateinformation stored in the storage with the new communication stateinformation, and estimates a new available bandwidth based on the newcommunication state information stored in the storage.

Yet another aspect of the present invention provides a code amountcontrol method for controlling a code amount used in encoding an imageto generate an image data and transmitting the image data to an imagereception apparatus via a communication path including a wirelesssection, the method comprising:

estimating a current available bandwidth based on historicalcommunication state information which is information on a pastcommunication state stored in a storage and controlling the code amountused in encoding the image; and

upon occurrence of communication path switching, acquiring a temporaryavailable bandwidth value corresponding to a new communication path,generating new communication state information corresponding to a newcommunication state based on the temporary available bandwidth value,replacing the historical communication state information stored in thestorage with the new communication state information, and estimating anew available bandwidth based on the new communication state informationstored in the storage.

Effect of the Invention

According to the present invention, upon occurrence of communicationpath switching, new communication state information is generated basedon a temporary available bandwidth value corresponding to a newcommunication path, and an available bandwidth is estimated based on thenew communication state information corresponding to a new communicationstate. This configuration enables efficient utilization of an availablebandwidth by properly estimating the available bandwidth even when theavailable bandwidth significantly changes upon occurrence ofcommunication path switching.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a general configuration of an imagetransmission system according to a first embodiment of the presentinvention;

FIG. 2 is a block diagram showing a schematic configuration of an imagetransmission apparatus 1;

FIG. 3 is a block diagram showing a schematic configuration of an imagereception apparatus 2;

FIG. 4 is an explanatory view showing an averaging operation performedby an available bandwidth estimator 24;

FIG. 5 is an explanatory view showing an example of how an availablebandwidth changes and how packet losses occur;

FIG. 6 is a flowchart showing operation procedures of the availablebandwidth estimator 24;

FIG. 7 is a flowchart showing an operation procedure of the availablebandwidth estimator 24;

FIG. 8 is an explanatory view showing examples of how counters in apacket loss counter 27 operate;

FIG. 9 is a flowchart showing operation procedures of the packet losscounter 27; and

FIG. 10 is a flowchart showing an operation procedure of the packet losscounter 27.

DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

A first aspect of the present invention made to achieve theabove-described object is an image transmission apparatus fortransmitting an image data to an image reception apparatus via acommunication path including a wireless section, the image transmissionapparatus comprising:

a communicator configured to transmit the image data to the imagereception apparatus;

a storage configured to store historical communication state informationwhich is information on a past communication state; and

a controller configured to estimate a current available bandwidth basedon the historical communication state information to control a codeamount used in encoding an image,

wherein, upon occurrence of communication path switching, the controlleracquires a temporary available bandwidth value corresponding to a newcommunication path, generates new communication state informationcorresponding to a new communication state based on the temporaryavailable bandwidth value, replaces the historical communication stateinformation stored in the storage with the new communication stateinformation, and estimates a new available bandwidth based on the newcommunication state information stored in the storage.

According to the first aspect of the present invention, upon occurrenceof communication path switching, new communication state information isgenerated based on a temporary available bandwidth value correspondingto a new communication path, and an available bandwidth is estimatedbased on the new communication state information corresponding to a newcommunication state. This configuration enables efficient utilization ofan available bandwidth by properly estimating the available bandwidtheven when the available bandwidth significantly changes upon occurrenceof communication path switching.

A second aspect of the present invention is the image transmissionapparatus of the first aspect, wherein the communicator receives a pathswitching notification transmitted from a communication controlapparatus located on the communication path, and

wherein the controller acquires the temporary available bandwidth valuecorresponding to the available bandwidth from the path switchingnotification.

According to the second aspect of the present invention, thecommunicator can acquire a temporary available bandwidth value which isproperly determined by the communication controller which grasps acommunication state of a new communication path.

A third aspect of the present invention is the image transmissionapparatus of the first aspect, wherein the controller uses apredetermined table to generate the new communication state informationfrom the temporary available bandwidth value.

According to the third aspect of the present invention, newcommunication state information can be generated with reduced processingload.

A fourth aspect of the present invention is the image transmissionapparatus of the first aspect, wherein the controller acquires apredetermined number of detection values representing an amount ofoccurrence of packet losses up to a present time, performs weightedaveraging of the predetermined number of detection values by usingweighting factors to provide an average number of detection values, andcalculates an estimated available bandwidth from the average number ofdetection values by using a predetermined calculation formula, andimmediately after the communication path switching, the controllertransits from a normal state to a transient state, in which theweighting factors to be used are changed to weighting factors for thetransient state.

According to the fourth aspect of the present invention, finaldetermination of the available bandwidth can be accelerated.

A fifth aspect of the present invention is the image transmissionapparatus of the fourth aspect, wherein, when the controller is in thetransient state, the controller performs the weighted averaging of thepredetermined number of detection values by multiplying each newdetection value by a larger weighting factor than a corresponding oneused in the normal state, and multiplying each old detection value by asmaller weighting factor than a corresponding one used in the normalstate.

According to the fifth aspect of the present invention, finaldetermination of the available bandwidth can be accelerated by using alarger weighting factors for a new detection(s) value so that the newdetection value make a more contribution in magnitude to the result ofavailable bandwidth estimation. In some cases, the weighting factors forold detection values may be made zero so that the old detection valuesare ignored in the available bandwidth estimation.

A sixth aspect of the present invention is the image transmissionapparatus of the fourth aspect, wherein the controller returns to thenormal state when a predetermined time has elapsed after the transitionto the transient state.

According to the sixth aspect of the present invention, the controllercan return to the normal state at an appropriate time.

A seventh aspect of the present invention is the image transmissionapparatus of the fourth aspect, wherein the controller returns to thenormal state when a number of detected packet losses exceeds apredetermined threshold.

According to the seventh aspect of the present invention, the controllercan return to the normal state at an appropriate time.

An eighth aspect of the present invention is the image transmissionapparatus of the fourth aspect, wherein the controller returns to thenormal state when a number of packets successively received after oneoccurrence of a packet loss exceeds a value assumed from the estimatedavailable bandwidth.

According to the eighth aspect of the present invention, the controllercan return to the normal state at an appropriate time.

A ninth aspect of the present invention is the image transmissionapparatus of the fourth aspect, wherein the controller returns to thenormal state when a number of packets successively received after oneoccurrence of a packet loss exceeds a value assumed from the estimatedavailable bandwidth.

According to the ninth aspect of the present invention, the controllercan return to the normal state at an appropriate time.

A tenth aspect of the present invention is the image transmissionapparatus of the first aspect, wherein, when estimating an estimatedavailable bandwidth based on an amount of occurrence of packet losses,the controller determines whether or not each packet loss is a randompacket loss caused by external noise in the wireless section, and whenthe packet loss is determined to be a random packet loss, the controllereliminates the packet loss in estimation of the estimated availablebandwidth.

According to the tenth aspect of the present invention, thisconfiguration can prevent the estimated available bandwidth fromsignificantly decreasing due to a random packet loss caused by externalnoise in the wireless section, thereby leading to inefficientutilization of the available bandwidth.

An eleventh aspect of the present invention is an image transmissionapparatus for transmitting an image data to an image reception apparatusvia a communication path including a wireless section, the imagetransmission apparatus comprising:

a communicator configured to transmit the image data to the imagereception apparatus;

a storage configured to store a past available bandwidth; and

a controller configured to estimate a current available bandwidth basedon the past available bandwidth to control a code amount used inencoding an image,

wherein, upon occurrence of communication path switching, the controlleracquires a temporary available bandwidth value corresponding to a newcommunication path, and estimates a new available bandwidth based on thetemporary available bandwidth value.

This configuration enables efficient utilization of an availablebandwidth by properly estimating the available bandwidth even when theavailable bandwidth significantly changes upon occurrence ofcommunication path switching as in the first aspect of the presentinvention.

A twelfth aspect of the present invention is an image transmissionsystem for transmitting an image data from an image transmissionapparatus to an image reception apparatus via a communication pathincluding a wireless section,

wherein the image transmission apparatus comprises:

a communicator configured to transmit the image data to the imagereception apparatus;

a storage configured to store historical communication state informationwhich is information on a past communication state; and

a controller configured to estimate a current available bandwidth basedon the historical communication state information to control a codeamount used in encoding an image;

wherein, upon occurrence of communication path switching, the controlleracquires a temporary available bandwidth value corresponding to a newcommunication path, generates new communication state informationcorresponding to a new communication state based on the temporaryavailable bandwidth value, replaces the historical communication stateinformation stored in the storage with the new communication stateinformation, and estimates a new available bandwidth based on the newcommunication state information stored in the storage.

This configuration enables efficient utilization of an availablebandwidth by properly estimating the available bandwidth even when theavailable bandwidth significantly changes upon occurrence ofcommunication path switching as in the first aspect of the presentinvention.

A thirteenth aspect of the present invention is a code amount controlmethod for controlling a code amount used in encoding an image togenerate an image data and transmitting the image data to an imagereception apparatus via a communication path including a wirelesssection, the method comprising:

estimating a current available bandwidth based on historicalcommunication state information which is information on a pastcommunication state stored in a storage and controlling the code amountused in encoding the image; and

upon occurrence of communication path switching, acquiring a temporaryavailable bandwidth value corresponding to a new communication path,generating new communication state information corresponding to a newcommunication state based on the temporary available bandwidth value,replacing the historical communication state information stored in thestorage with the new communication state information, and estimating anew available bandwidth based on the new communication state informationstored in the storage.

This configuration enables efficient utilization of an availablebandwidth by properly estimating the available bandwidth even when theavailable bandwidth significantly changes upon occurrence ofcommunication path switching as in the first aspect of the presentinvention.

Embodiments of the present invention will be described below withreference to the drawings.

First Embodiment

FIG. 1 is a diagram showing a general configuration of an imagetransmission system according to a first embodiment of the presentinvention.

The image transmission system includes an image transmission apparatus1, an image reception apparatus 2, and a communication controller 3. Theimage transmission apparatus 1 configured to perform image transmissionto the image reception apparatus 2 via a heterogeneous network.

The heterogeneous network includes, in addition to one or more basestations utilizing existing wireless communication methods (e.g. accesspoints for cellular communications such as LTE or those for WiFi(Registered Trademark)), one or more access points for cellularcommunications utilizing a high SHF (Super High Frequency) band proposedin 5G communication technology and/or access points for WiGig(Registered Trademark) communications utilizing millimeter bands. Theimage transmission apparatus 1 performs image transmission usingmultiple communication paths via these base stations and/or accesspoints.

The communication controller 3 is configured to control communicationswhich the image transmission apparatus 1 performs using multiplecommunication paths via these base stations and/or access points in theheterogeneous network, which may serve as, for example, a macro cellbase station covering a wide communication area.

Next, the image transmission apparatus 1 will be described. FIG. 2 is ablock diagram showing a schematic configuration of the imagetransmission apparatus 1.

The image transmission apparatus 1 includes an image input 11, acommunicator 12, a controller 13, and a storage 14.

The image input 11 receives image data provided from a camera 5.

The communicator 12 communicates with the image reception apparatus 2via a communication path. For example, the communicator transmits imagepackets to the image reception apparatus 2, and receives receptionquality information; that is, a communication state monitoring packet(RTCP-RR, including transmission time information) transmitted from theimage reception apparatus 2. Furthermore, the communicator 12communicates with the communication controller 3, and receives, forexample, a handover notification transmitted from the communicationcontroller 3.

The storage 14 stores communication state information (packet loss rate,delay time, transmission data amount, and other information), which ishistorical communication state information i.e. information on a pastcommunication state(s) (during the past several seconds). Thecommunication state information is updated as needed. The storage 14stores a table used in processing operations such as available bandwidthestimation performed by the controller 13. Moreover, the storage 14stores programs to be executed by the controller 13.

The controller 13 includes an image encoder 21, a packetizer 22, acommunication state monitor 23, an available bandwidth estimator 24, anencoding controller 25, a historical information rewriter 26, and apacket loss counter 27. The controller 13 is implemented by a processor,and each part of the controller 13 is implemented by causing theprocessor to execute a program stored in the storage 14.

The image encoder 21 encodes the image data received by the image input11 using a predetermined compression method (for example, H.264 orH.265).

The packetizer 22 divides image codes, which are generated by the imageencoder 21, into packets using RTP (Real-time Transport Protocol) or anyother suitable method. Moreover, the packetizer 22 notifies thecommunication state monitor 23 of transmission data amounts.

The communication state monitor 23 works cooperatively and communicatescommunication state monitoring packets, such as RTCP (RTP ControlProtocol) based packets, with the image reception apparatus 2 to acquirecommunication state information (such as packet loss rate and delaytime) included in a received communication state monitoring packet(RTCP-RR), and then notifies the available bandwidth estimator 24 of theacquired communication state information.

The available bandwidth estimator 24 estimates the available bandwidthof a current communication path based on the current communication stateinformation acquired by the communication state monitor 23 and the pastcommunication state information stored in the storage 14 as historicalinformation. In the present embodiment, an available bandwidth isestimated based on communication state information (delay time (RTT) andpacket loss rate) according to TFRC (TCP-Friendly Rate Control)specified in RFC 5348/3448.

The encoding controller 25 determines the code amount (compression rate)and resolution used in encoding an image based on the estimatedavailable bandwidth acquired by the available bandwidth estimator 24,and then instructs the image encoder 21 to perform encoding operationsaiming for the code amount and resolution.

The historical information rewriter 26 acquires, based on the handovernotification received by the communicator 12, a temporary availablebandwidth value corresponding to a new communication path. Then, basedon the temporary available bandwidth value, the historical informationrewriter 26 generates new communication state information appropriate toa new communication state, and then stores the new communication stateinformation in the storage 14. Specifically, the historical informationrewriter causes the previous communication state information stored inthe storage 14 to be discarded and replaced with the new communicationstate information.

The packet loss counter 27 counts packet losses that occur within apredetermined time, and notifies the available bandwidth estimator 24 ofthe count result; that is, the number of detected packet losses. In thisparticular embodiment, the packet loss counter 27 determines whether ornot each packet loss is a random packet loss caused by external noise inthe wireless section, and if a packet loss is determined to be a randompacket loss, the packet loss counter 27 eliminates the packet loss fromthe count result.

Next, the image reception apparatus 2 will be described. FIG. 3 is ablock diagram showing a schematic configuration of the image receptionapparatus 2.

The image reception apparatus 2 includes a communicator 31, an imageoutput 32, a controller 33, and a storage 34.

The communicator 31 communicates with the image transmission apparatus1. For example, the communicator 31 receives image packets and acommunication state monitoring packet (RTCP-SR, including reception timeinformation) transmitted from the image transmission apparatus 1, andthe communicator 31 transmits a communication state monitoring packet(RTCP-RR, including transmission time information) to the imagetransmission apparatus 1.

The storage 34 stores image packets received by the communicator 31and/or image data generated by the controller 33. Moreover, the storage34 stores programs to be executed by the controller 33.

The image output 32 outputs image data generated by the controller 33 toa display 6.

The controller 33 includes a packet disassembler 41, an image decoder42, and a communication state monitor 43. The controller 33 isimplemented by a processor, and each part of the controller 33 isimplemented by causing the processor to execute a program stored in thestorage 34.

The packet disassembler 41 disassembles image packets received by thecommunicator 31 to provide image codes. Furthermore, the packetdisassembler 41 notifies the communication state monitor 43 of an amountof received data and a number of detected packet losses.

The image decoder 42 decodes the image codes provided from the packetdisassembler 41 to output an image data. The image decoder 42 performsthis decoding operation based on resolution information included in codedata, and thus, when receiving image packets with a resolution differentfrom the size designated by the resolution information, the imagedecoder 42 changes the resolution of the image by resizing the image toa proper display image size.

The communication state monitor 43 works cooperatively and communicatescommunication state monitoring packets, which are RTCP (RTP ControlProtocol) packets, with the image transmission apparatus 1 to acquirecurrent communication state information (such as packet loss rate anddelay time). Then, the communication state monitor 43 measures a delaytime of the communication state monitoring packets based on the timestamps thereof, and measures a number of packet losses based on thesequence numbers on the communication state monitoring packets. Then,the communication state monitor 43 transmits a communication statemonitoring packet (RTCP-RR) including the acquired communication stateinformation to the image transmission apparatus 1.

Next, processing operations performed by the available bandwidthestimator 24 of the image transmission apparatus 1 will be described.FIG. 4 is an explanatory view showing an averaging operation performedby the available bandwidth estimator 24.

The available bandwidth estimator 24 estimates an available bandwidthusing the following bandwidth calculation formula (Formula 1) defined byTFRC. This bandwidth calculation formula is used to calculate anavailable bandwidth (average throughput) from a packet loss rate and around-trip delay time (RTT) that are detected values representingoccurrence of packet losses.

$\begin{matrix}{T = \frac{S}{{d\sqrt{\frac{2\; p}{3}}} + {3\;{{p\left( {1 + {32\; p^{2}}} \right)} \cdot R}\sqrt{\frac{3\; p}{8}}}}} & (1)\end{matrix}$

-   T=average throughput-   S=packet size-   R=TCP retransmission timeout value (4×RTT)-   d=round-trip delay time between transmitter and receiver (RTT)-   p=packet loss rate

The packet loss rate is given by an inverse of the number ofsuccessively received packets (packet loss period), and determined bymonitoring packet reception to count the number of successively receivedpackets; that is, the number of successively and normally receivedpackets without any packet loss.

A counter is provided to count normally received packets, and, upondetection of a packet loss, the counter is reset. The availablebandwidth estimator 24 repeats the count operation to acquire the numberof successively received packets (packet loss period) for eachoperation. When packet losses occur several times successively, suchsuccessive packet losses are counted as one packet loss event.

In order to avoid a significant change in the estimated availablebandwidth in response to an occurrence of a packet loss, the availablebandwidth estimator 24 performs weighted averaging of packet lossperiods (the number of successively received packets) for apredetermined number of times (for example, eight times).

Specifically, first, the available bandwidth estimator 24 performsweighted averaging of the current packet loss period (the number ofsuccessively received packets) and the packet loss periods of theprecedent seven times to provide an average value of the packet lossperiods. The available bandwidth estimator 24 also performs weightedaveraging of the past eight packet loss periods to provide an averagevalue of the packet loss periods of the past eight times. Then, theavailable bandwidth estimator 24 chooses the larger one (not smallerone) of the two average values as an average packet loss period, anddetermines the packet loss rate, which is an inverse of the averagepacket loss period.

In this example, the weighting factors are as follows:

{1.0, 1.0, 1.0, 1.0, 0.8, 0.6, 0.4, 0.2}.

These weighting factors are arranged in order from newest to oldest.

Next, processing operations performed by the historical informationrewriter 26 of the image transmission apparatus 1 will be described.FIG. 5A is an explanatory view showing an example of how the availablebandwidth changes and FIG. 5B is an explanatory view showing an exampleof occurrences of packet losses (random loss and congestion losses).

In a heterogeneous network, narrow bandwidth/broad area communicationpaths and large bandwidth/small area communication paths are mixedlyprovided, and an available bandwidth can greatly change when a handover(communication path switching) occurs. For example, since LTE systemscan provide an available bandwidth of 5 Mbps (and a total capacity of100 Mbps) while WiGig (Registered Trademark) can provide an availablebandwidth of 1 Gbps (and a total capacity of 20 Gbps), when a handoveroccurs between these two types of communication paths, an availablebandwidth can change by two orders of magnitude.

According to a TFRC standard method, since, in order to estimate anavailable bandwidth based on communication state information (packetloss rate and delay time), historical communication state informationi.e. information on a past communication state(s) is used as a basis ofthe estimation, upon occurrence of communication path switching, anavailable bandwidth gradually increases in response to a change in thecommunication state information. Thus, it takes a long time to achieveefficient utilization of the actual available bandwidth.

Therefore, in the present embodiment, when a handover occurs, thecommunication controller 3 notifies the image transmission apparatus 1of the available bandwidth corresponding to a new communication path. Inresponse, the image transmission apparatus 1 generates new communicationstate information appropriate to the available bandwidth notified fromthe communication controller 3, and causes the previous communicationstate information stored in the storage 14 to be discarded and replacedwith the new communication state information. Then, the availablebandwidth estimator 24 estimates a new available bandwidth based on thenew communication state information (packet loss rate and delay time).

In this case, it is possible to obtain a packet loss rate (packet lossperiod) as part of the new communication state information by backcalculating a packet loss rate from the bandwidth calculation formula(Formula 1). However, this back calculating method uses a complicatedcalculation formula, resulting in high processing load. Thus, in thepresent embodiment, a table representing a relationship between anavailable bandwidth, a packet loss rate, and a delay time is created inadvance based on the bandwidth calculation formula, and the packet lossrate is determined from the temporary available bandwidth value by usingthis table.

The delay time (RTT) as part of the new communication state informationmay be the current delay time. In this way, the available bandwidthnotified by the communication controller 3, a current delay time, and apacket loss rate (packet loss period) are obtained.

It should be noted that, in the present embodiment, since averaging ofthe packet loss rates (packet loss periods) is performed, the samevalues are set as the communication state information stored in thestorage 14 a predetermined number of times (for example, eight times) inthe past.

In the present embodiment, the communication controller 3 addsinformation concerning a temporary available bandwidth valuecorresponding to a new (post-handover) communication path to a handovernotification, and then the communication controller 3 transmits thehandover notification to the image transmission apparatus 1. Thecommunication controller 3 may be configured to set a temporaryavailable bandwidth value (e.g., 5 Mbps in LTE) according to the type ofcommunication path (such as LET) of the new communication path. Thecurrent available bandwidth may be estimated based on a congestiondegree and/or the historical communication state information (delay timeand packet loss rate). Moreover, the available bandwidth may be measuredduring a negotiation immediately after handover. In this case, sinceuser data cannot be transmitted during handover, data used formeasurement (probe) may be transmitted so that the communication statecan be measured.

In this way, in the present embodiment, since the available bandestimation is started in consideration of new communication stateinformation appropriate to an available bandwidth corresponding to a new(post-handover) communication path, the estimated available bandwidthcan be made closer to the actual value of available bandwidth, andefficient utilization of the available bandwidth can be achieved.

At system startup, it is possible to use an initial available bandwidthvalue stored in advance as initial setting information in the storage14, and the subsequent operations can be performed in the same manner asin the case of handover.

Next, processing operations performed by the available bandwidthestimator 24 of the image transmission apparatus 1 will be described.

In the present embodiment, upon occurrence of handover, pastcommunication state information i.e. historical communication stateinformation is discarded and replaced with new communication stateinformation appropriate to an available bandwidth of a new(post-handover) communication path, and the new communication stateinformation is used as a basis of estimation of an available bandwidth,thereby allowing the estimated available bandwidth to be made closer tothe actual value of available bandwidth. However, if the subsequentoperations for available band estimation are performed according to theTFRC standard method, it takes a long time to finally determine theestimated value of available bandwidth (See FIG. 5).

Therefore, in the present embodiment, the controller 13 is configuredto, immediately after handover, transit to a transient state in whichestimation operations are modified to accelerate the final determinationof available bandwidth. In the transient state, the parameters used foravailable bandwidth estimation are changed from those for a normal stateaccording to the TFRC standard method. Specifically, the weightingfactors used in the weighted averaging of packet loss periods (packetloss rates) are changed.

The weighting factors are preset and contained in factor tables storedin the storage 14. The storage 14 stores factor tables for the normalstate and the transient state, respectively, and immediately afterhandover, the factor table to be used is switched from one for thenormal state to one for the transient state.

The weighting factor for the normal state and the weighting factor forthe transient state may be set, for example, as follows.

Normal state: {1.0, 1.0, 1.0, 1.0, 0.8, 0.6, 0.4, 0.2}

Transient state: {4.0, 1.0, 1.0, 0.0, 0.0, 0.0, 0.0, 0.0}

In the transient state, factors for new values are set higher valueswhile those for old values are set to 0. In other words, weights aregiven to the new values and the old values are ignored in thecalculation.

In this way, in the present embodiment, immediately after handover,control is performed so as to temporarily change the parameters used foravailable bandwidth estimation. Thus, immediately after the handover,when the actual value of the available bandwidth is smaller than thatnotified from the communication controller 3, the estimated value of theavailable bandwidth is promptly increased, thereby enabling efficientutilization of available bandwidths.

Furthermore, in the present embodiment, when, after the controller 13transits to the transient state, any of predetermined return conditionsis met, the controller 13 returns to the normal state. The returnconditions being met means that the final determination of the estimatedavailable bandwidth has been substantially made such that efficientutilization of available bandwidths is adequately achieved or thatcongestion is occurring because the estimated value of the availablebandwidth is excessively increased. When such a condition is met, thecontroller 13 promptly returns to the normal condition.

In the present embodiment, as a first return condition, when apredetermined time (for example, 30 seconds) elapses after thetransition from the normal state to the transient state, the controller13 returns to the normal state. As a second return condition, when thenumber of detected packet losses exceeds a predetermined threshold value(for example, twice), the controller 13 returns to the normal state. Asa third return condition, when, after a packet loss occurs once, thenumber of successively received packets (packet loss period) exceeds avalue assumed from the current estimated available bandwidth, thecontroller 13 returns to the normal state. As a fourth return condition,when a predetermined time (for example, 10 seconds) elapses after apacket loss occurs once, the controller 13 returns to the normal state.When any one of the first to fourth return conditions is met, thecontroller 13 returns to the normal state.

The number of detected packet losses is the number of occurrences ofpacket loss events, and multiple successive packet losses are counted asone packet loss. Moreover, if a packet loss event is determined to be arandom loss, the controller 13 eliminates the packet loss. Thus, thenumber of occurrences of the packet loss events is the number ofoccurrences of congestion losses.

In the present embodiment, when any one of the first to fourth returnconditions is met, the controller 13 returns to the normal state.However, one of the first to fourth return conditions or any combinationthereof may be used as a return condition.

In this way, when the controller 13 returns to the normal state, theavailable bandwidth estimator 24 performs available bandwidth estimationaccording to the TFRC standard method.

In this way, in the present embodiment, since the control quicklyreturns to one according to the TFRC standard method, consistency andfairness with other users' communications can be secured. Further, sincethe same bandwidth calculation formula defined by TFRC is used in bothof the transient state and the normal state, when the controller 13returns from the transient state to the normal state, continuity of theestimated available bandwidth value can be maintained.

Next, operation procedures of the available bandwidth estimator 24 ofthe image transmission apparatus 1 will be described. FIGS. 6 and 7 areflowcharts showing operation procedures of the available bandwidthestimator 24.

First, operations performed when a handover occurs and the communicator12 receives a handover notification will be described. As shown in FIG.6A, the controller 13 acquires a temporary available bandwidth value ofa new (post-handover) communication path included in a handovernotification (ST101).

Next, the controller 13 deletes the communication state information(historical information) stored in the storage 14 (ST102). Then, thecontroller 13 generates new communication state information based on thetemporary available bandwidth value notified from the communicationcontroller 3 and stores the new communication state information in thestorage 14 as historical information (ST103). In this case, thecontroller 13 calculates the communication state information byback-calculation from the available bandwidth.

Next, a timer starts timing measurement (ST104).

Next, the controller 13 switches the factor table to be used foravailable band estimation from the factor table for the normal state toone for the transient state (ST105). In this way, the controller 13transits to the transient state.

Next, the available bandwidth estimator 24 estimates an availablebandwidth based on the communication state information (historicalinformation) (ST106). Then, the encoding controller 25 determines a codeamount and a resolution based on the estimated value of the availablebandwidth (ST107). Then, the encoding controller 25 instructs the imageencoder 21 to perform encoding operations aiming for the determined codeamount and resolution (ST108).

Next, an operation procedure performed when the timer expires, that is,when a predetermined time (for example, 30 seconds) elapses after thetransition from the normal state to the transient state will bedescribed. First, as shown in FIG. 6B, the controller 13 returns thefactor table to be used from the one for the transient date to one forthe normal state (ST111). Thus, the controller 13 returns to the normalstate, and the available bandwidth estimator 24 estimates an availablebandwidth using the table for the normal state (ST112). Then, theencoding controller 25 determines a code amount and a resolution (ST113)and instructs the image encoder 21 to perform encoding operations(ST114).

Next, an operation procedure performed when the communicator 12 receivesa communication state monitoring packet transmitted from the imagereception apparatus 2 will be described. As shown in FIG. 7, thecontroller 13 acquires communication state information (delay time,number of detected packet losses and number of received packets)included in a received state monitoring packet (ST121). Then, thecontroller 13 updates the communication state information (historicalinformation) stored in the storage 14 (ST122).

Next, the controller 13 determines whether or not the number of detectedpacket losses exceeds a predetermined threshold (for example, twice)(ST123).

If the number of detected packet losses is equal to or less than thethreshold (No in ST123), the controller 13 remains in the transientstate, and the available bandwidth estimator 24 estimates an availablebandwidth using the factor table for the transient state (ST106), andthen the controller 13 determines a code amount and a resolution (ST107)and instructs the image encoder 21 to perform encoding operations(ST108).

If the number of detected packet losses exceeds the threshold (Yes inST123), the controller 13 returns the factor table used for availablebandwidth estimation from one for the transient state to one for thenormal state (ST111). As a result, the controller 13 returns to thenormal state, and the available bandwidth estimator 24 estimates anavailable bandwidth using the factor table for normal state (ST112), andthen the controller 13 determines a code amount and a resolution (ST113)and instructs the image encoder 21 to perform encoding operations(ST114).

In the example shown in FIG. 7, the controller 13 is configured suchthat, if a predetermined time (for example, 30 seconds) elapses afterthe transition from the normal state to the transient state, or if thenumber of detected packet losses exceeds a predetermined thresholdvalue, the controller 13 returns to the normal state. In some cases, thecontroller 13 may be configured such that, if the number of successivelyreceived packets (packet loss period) exceeds a value assumed from thecurrent estimated available bandwidth after a packet loss occurs once,or if a predetermined time (for example, 10 seconds) elapses after apacket loss occurs once, the controller 13 returns to the normal state.

Next, operations of the packet loss counter 27 of the image transmissionapparatus 1 will be described. FIG. 8 is an explanatory view showingexamples of how counters in the packet loss counter 27 operate.

In the present embodiment, the available bandwidth estimator 24estimates an available bandwidth according to how packet losses occur.Specifically, the available bandwidth estimator 24 estimates anavailable bandwidth based on the packet loss rate. Thus, once a packetloss occurs, the estimated value of the available bandwidthsignificantly decreases.

Packet losses include a packet loss caused by congestion (congestionloss) and a packet loss caused by external noise (random loss). Acongestion loss occurs when an amount of transmission exceeds anavailable bandwidth capacity, whereas a random loss can occur even whenan amount of transmission does not exceed an available bandwidthcapacity. Thus, if the controller 13 is configured to, upon occurrenceof packet losses, narrow an available bandwidth in the same wayregardless of the type of packet loss, the available bandwidth can benarrowed even when a random loss occurs and an amount of transmissiondoes not exceeds an available bandwidth capacity, which leads toinefficient utilization of available bandwidths (See FIG. 5).

In other words, as occurrence of a congestion loss reflects an actualavailable bandwidth, the controller 13 needs to narrow an availablebandwidth in response to occurrence of a congestion loss, and asoccurrence of a random loss does not reflect an actual availablebandwidth, the controller 13 does not need to narrow an availablebandwidth in response to occurrence of a random loss.

Thus, in the present embodiment, in order to avoid the unnecessaryreduction of available bandwidth in response to such random losses, thecontroller 13 determines whether or not a detected packet loss is arandom loss, and when the packet loss is determined to be a random loss,the controller 13 controls such that the packet loss detection resultdoes not affect the available bandwidth estimation.

According to the TFRC standard method, when a packet loss occurs, acounter for counting the number of successively and normally receivedpackets (the number of successively received packets) is reset. However,in the present embodiment, if the packet loss is determined to be arandom loss, the controller 13 does not reset the counter for countingthe number of successively received packets. In this way, this canprevent the packet loss detection result from affecting the availablebandwidth estimation.

With regard to the determination of the type of a detected packet loss,a packet loss is determined to be a random loss if it is detected whenthe frequency of occurrence of packet loss is low, and a packet loss isdetermined to be a congestion loss if it is detected when the frequencyof occurrence of packet loss is high.

Specifically, a detected packet loss is determined to be a random lossif it is detected when the packet loss occurrence interval exceeds apredetermined threshold. In some cases, the threshold is a packet lossrate assumed from the estimated current available bandwidth, and adetected packet loss is determined to be a random loss if the packetloss rate exceeds the threshold. In some cases, the threshold is thenumber of successively received packets (packet loss period) assumedfrom the estimated current available bandwidth, and a detected packetloss is determined to be a random loss if it is detected when the numberof successively received packets exceeds the threshold.

The threshold value used to determine whether or not a packet loss is arandom loss can be obtained from the estimated current availablebandwidth by using a predetermined calculation formula.

In the present embodiment, the packet loss counter includes threecounters which are configured to count the number of successivelyreceived packets, count the actual number of successively receivedpackets, and count the number of random loss detections, respectively.

The counter for counting the number of successively received packetscounts the number of successively and normally received packets, and thecounter value of this counter i.e. the number of successively receivedpackets (packet loss period) is used for the available bandwidthestimation. The counter for counting the actual number of successivelyreceived packets counts the actual number of successively and normallyreceived packets, and is used to determine the type of packet loss. Thecounter for counting the number of random loss detections counts thenumber of the random losses after the latest congestion loss occurs.

In the following description, C0 denotes the number of successivelyreceived packets, which is a count value of the counter therefor, C1denotes the actual number of successively received packets, which is acount value of the counter therefor, and C2 denotes the number of randomloss detections, which is a count value of the counter therefor.

When a packet loss occurs, the counter for counting the actual number ofsuccessively received packets C1 is reset. Then, the controller 13compares the current number of successively received packets C0 with areference value (T×C2) obtained by multiplying an assumed packet lossperiod T by the current number of random loss detections C2, and, if thecurrent number of successively received packets C0 does not exceed thereference value (T×C2), a packet loss is determined to be a congestionloss. The assumed packet loss period T is assumed from the currentavailable bandwidth, and may be calculated from the current availablebandwidth using a predetermined table or calculation formula. If it is acongestion loss, the counter for counting C0 (the number of successivelyreceived packets) and the counter for counting C2 (the number of randomloss detections) are reset.

In the example shown in FIG. 8, packet losses occur at times T1, T2, andT3 after the occurrence of handover. The counter for counting C1 (theactual number of successively received packets) is cleared at thesetimes T1, T2, and T3, respectively. Then, a communication statemonitoring packet (RTCP-RR) is received at time T4.

In the present embodiment, random loss determination is performed inresponse to receiving a communication state monitoring packet (RTCP-RR),and in the example shown in FIG. 8, random loss determination isperformed at time T4 when the communication state monitoring packet isreceived.

In this case, at time T1, the number of successively received packets C0is the same as the actual number of successively received packets C1 andexceeds the reference value (T×C2 (=1)), and thus, the packet loss isregarded as a random loss, and the number of random loss detection C2 isone. At time T2, the number of successively received packets C0 is thesame as the actual number of successively received packets C1, andexceeds the reference value (T×C2 (=2)), and thus, the packet loss isregarded as a random loss, and the number of random loss detection C2 isone. At times T1 and T2, the counter for counting the actual number ofsuccessively received packets C1 is cleared and the counter for countingthe number of successively received packets C0 is not cleared.

At time T3, the number of successively received packets C0 is the sameas the actual number of successively received packets C1 and does notexceed the reference value (T×C2 (=3)), and thus the packet loss isregarded as a congestion loss and the counter for counting the number ofrandom loss detections C2 is cleared. Moreover, the counter for countingthe actual number of successively received packets C1 and the counterfor counting the number of successively received packets C0 are cleared.After being cleared, the initial value of the counter for counting theactual number of successively received packets C1 is the number ofreceived packets notified by the communication state monitoring packet.

On the assumption on that packets have been normally received before thehandover, the actual number of the successively received packets C1 is asufficiently large value (100,000 or more or 60 seconds or more).

In the example shown in FIG. 8, multiple successive packet losses occurat time T5. At T5, the number of random loss detections C2 is N and thenumber of successively received packets C0 does not exceed the referencevalue (T×C2), and thus the packet losses are regarded as congestionlosses and the counter for counting the number of random loss detectionsC2 is cleared. Moreover, the counter for counting the actual number ofsuccessively received packets C1 and the counter for counting the numberof successively received packets C0 are cleared.

Next, operation procedures of the packet loss counter 27 of the imagetransmission apparatus 1 will be described. FIGS. 9 and 10 areflowcharts showing operation procedures of the packet loss counter 27.

First, an initialization operation will be described. At this step, thecounters are initialized as shown in FIG. 9A. The counter for countingthe number of successively received packets C0, the counter for countingthe actual number of successively received packets C1, and the counterfor counting the number of random loss detections C2 are initialized;that is, the number of successively received packets C0, the actualnumber of successively received packets C1, and the number of randomloss detections C2 are set to 0 (ST201).

Then, an operation procedure performed when a handover occurs and thecommunicator 12 receives a handover notification will be described. Asshown in FIG. 9B, first, the packet loss counter acquires an availablebandwidth of a new (post-handover) communication path included in thehandover notification (ST211). Next, the packet loss counter 27 acquiresa packet loss rate and a packet loss period T assumed from the currentavailable bandwidth (ST212). Then, the counter for counting the numberof successively received packets C0 and the counter for counting theactual number of successively received packets C1 are set to the packetloss period T (ST213).

In this way, since the controller 13 is in the transient stateimmediately after handover, the counters are set to values assumed fromthe available bandwidth notified from the communication controller 3regardless of an amount of occurrence of packet losses.

At system startup, the packet loss counter 27 operates in the samemanner as when receiving a handover notification shown in FIG. 9B.

Next, operations of the packet loss counter 27 when the communicator 12receives a communication state monitoring packet will be described.First, as shown in FIG. 10, the packet loss counter 27 acquirescommunication state information (i.e. the number of received packets Rand the number of detected packet loss detections L) included in thecommunication state monitoring packet (ST221). Next, the packet losscounter 27 acquires an estimated value of available bandwidth (ST222).Then, the packet loss counter 27 acquires an assumed packet loss rateand an assumed packet loss period T assumed from the estimated availablebandwidth (ST223).

Next, the packet loss counter 27 determines whether the number of packetloss detections L is a positive number or not; that is, whether or notthere is a packet loss (ST224).

If there is no packet loss (No in ST224), the counter for counting thenumber of successively received packets C0 is set to a value obtained byadding the number of received packets R to the number of successivelyreceived packets C0. The counter for counting the actual number ofsuccessively received packets C1 is set to a value obtained by addingthe number of received packets R to the actual number of successivelyreceived packets C1 (ST225).

Next, the packet loss counter 27 notifies the available bandwidthestimator 24 of the number of packet loss detections L (ST226). As aresult, the available bandwidth estimator 24 is allowed to calculate anestimated available bandwidth using the number of packet loss detectionsL.

If there is a packet loss (Yes in ST224), the counter for counting thenumber of random loss detections C2 is set to a value obtained by addingthe number of packet loss detections L to the number of random lossdetections C2 (ST227).

Next, a timer starts timing measurement (ST228).

The packet loss counter 27 determines whether or not a previous timervalue (an elapsed time since the previous packet loss detection), i.e. apacket loss occurrence interval, exceeds a predetermined threshold (forexample, 60 seconds) (ST229).

If the previous timer value is less than or equal to the threshold (Noin ST229), next, the packet loss counter 27 determines whether or notthe actual number of successively received packets C1 exceeds apredetermined threshold (for example, 100,000) (ST230). This thresholdis determined based on a packet loss rate assumed in regard to thecommunication path.

If C1 is less than or equal to the threshold (No in ST230), next, thepacket loss counter 27 determines whether or not the number ofsuccessively received packets C0 exceeds a value (C2×T) obtained bymultiplying the number of random loss detections C2 by the assumedpacket loss period T determined from the current estimated bandwidth(ST231).

If the number of successively received packets C0 exceeds the value(C2×T) (No in ST231), the packet loss counter 27 determines that thepacket loss is a congestion loss. Then, the counter for counting theactual number of successively received packets C1 and the counter forcounting the number of successively received packets C0 are both cleared(initialized) so that the number of successively received packets C0 andthe actual number of successively received packets C1 are set to thenumber of received packets R notified by an RTCP-RR packet. The counterfor counting the number of random loss detections C2 is cleared; thatis, the number of random loss detections C2 is set to 0 (ST232). Then,the packet loss counter 27 notifies the available bandwidth estimator 24of the number of packet loss detections L (ST226).

If the previous timer value exceeds the threshold (Yes in ST229), theactual number of successively received packets C1 is less than or equalto the threshold (Yes in ST230), and the number of successively receivedpackets C0 is less than or equal to C2×T (Yes in ST231), the packet losscounter determines that the packet loss is a random loss. Then, only thecounter for counting the actual number of successively received packetsC1 is cleared (initialized) and C1 is set to the number of receivedpackets R acquired from an RTCP-RR packet. That is, the packet losscounter 27 determines that no packet loss is detected. The counter forcounting the number of successively received packets C0 is set to avalue obtained by adding the number of received packets R to the numberof successively received packets C0. The number of packet lossdetections L is set to 0 (ST233). Then, the packet loss counter 27notifies the available bandwidth estimator 24 of the number of packetloss detections L (ST226).

According to the present embodiment, even when a significant increase inavailable bandwidth occurs due to communication path switching, theabove-described control enables efficient utilization of availablebandwidths to increase a code amount used in encoding an image, therebyimproving image quality. Also, even when a significant decrease inavailable bandwidth occurs due to communication path switching, theabove-described control quickly allows for congestion avoidance so as toprevent an increase in delay time and prevent occurrence of packetlosses, thereby improving image quality.

Second Embodiment

Next, a second embodiment of the present invention will be described.Except for what will be discussed here, the configuration of the secondembodiment is the same as that of the first embodiment.

While, in the first embodiment, an available bandwidth is estimatedaccording to TFRC (TCP-Friendly Rate Control), in the second embodiment,available bandwidth estimation is conducted according to a methodadopting BCC (Binomial Congestion Control Algorithms).

According to a standard control method adopting BCC, a previous (past)available bandwidth w is stored as historical communication stateinformation i.e. information on a past communication state(s). Whenthere is no packet loss, after a predetermined time has elapsed, theavailable bandwidth w is incrementally increased as the followingequation (bandwidth calculation equation),w<=w+α/w{circumflex over ( )}k (α>0),and when there is a packet loss, immediately after a packet lossdetection, the available bandwidth w is reduced by multiplication as thefollowing equation,w<=w−(1−β)×w{circumflex over ( )}1(0<β<1),where k and 1 can be various combinations of values.

In the second embodiment, when a handover notification (path switchingnotification) is received, the previous (past) available bandwidth w(historical information) stored in the storage 14 is discarded andreplaced with an available bandwidth w0 notified from the communicationcontroller 3. Specifically, instead of w<=w+α/w{circumflex over ( )}k,w<=w0is used.

In the second embodiment, the controller 13 transits from the normalstate to the transient state triggered by occurrence of a handover inthe same manner as the first embodiment. However, the state transitionfrom the transient state to the normal state is controlled only by usinga timer without using packet loss detection result.

Furthermore, in the second embodiment, factors k and I (parameters) arechanged between the normal state and the transient state. Specifically,in the normal state, the factors (k, I)=(1, 0) are used, providingstable IIAD (Inverse-Increase/Additive Decrease), and in the transientstate immediately after handover. factors (k, I)=(0, 1) are used,providing AIMD (Additive-Increase/Multiplicative-Decrease), whichaccelerates final determination of the available bandwidth. In thetransient state after a predetermined time has elapsed from handover,factors (k, I)=(1/2, 1/2) are used, providing SQRT, which is relativelystable and accelerates final determination of the available bandwidth.Then, after a further predetermined time has elapsed, the controller 13returns to the normal state.

While specific embodiments of the present disclosure are describedherein for illustrative purposes, the present disclosure is not limitedthereto. It will be understood that various changes, substitutions,additions, and omissions may be made for elements of the embodimentswithout departing from the scope of the present invention. In addition,elements and features of the different embodiments may be combined witheach other as appropriate to yield an embodiment which is within thescope of the present invention.

INDUSTRIAL APPLICABILITY

An image transmission apparatus, an image transmission system, and acode amount control according to the present invention achieve theeffects to enables efficient utilization of an available bandwidth byproperly estimating the available bandwidth even when the availablebandwidth significantly changes upon occurrence of communication pathswitching, and are useful as an image transmission apparatus fortransmitting an image data to an image reception apparatus via acommunication path including a wireless section, an image transmissionsystem for transmitting an image data from an image transmissionapparatus to an image reception apparatus via a communication pathincluding a wireless section, and a code amount control method forcontrolling a code amount used in encoding an image to generate an imagedata and transmitting the image data to an image reception apparatus viaa communication path including a wireless section.

GLOSSARY

-   1 image transmission apparatus-   2 image reception apparatus-   3 user terminal (terminal apparatus)-   12 communicator-   13 controller-   14 storage-   21 image encoder-   22 packetizer-   23 communication state monitor-   24 available bandwidth estimator-   25 encoding controller-   26 historical information rewriter-   27 packet loss counter

The invention claimed is:
 1. An image transmission apparatus fortransmitting an image data to an image reception apparatus via acommunication path including a wireless section, the image transmissionapparatus comprising: a communication device configured to transmit theimage data to the image reception apparatus; a storage configured tostore historical communication state information which is information ona past communication state; and a processor configured to estimate acurrent available bandwidth based on the historical communication stateinformation to control a code amount used in encoding an image, wherein,upon occurrence of communication path switching, the processor acquiresa temporary available bandwidth value corresponding to a newcommunication path, generates new communication state informationcorresponding to a new communication state including at least one ofpacket loss rates and packet loss periods based on the temporaryavailable bandwidth value, replaces the historical communication stateinformation stored in the storage with the new communication stateinformation, and estimates a new available bandwidth based on the newcommunication state information stored in the storage.
 2. The imagetransmission apparatus according to claim 1, wherein the communicationdevice receives a path switching notification transmitted from acommunication control apparatus located on the communication path, andwherein the processor acquires the temporary available bandwidth valuecorresponding to the available bandwidth from the path switchingnotification.
 3. The image transmission apparatus according to claim 1,wherein the processor uses a predetermined table to generate the newcommunication state information from the temporary available bandwidthvalue.
 4. The image transmission apparatus according to claim 1, whereinthe processor acquires a predetermined number of detection valuesrepresenting an amount of occurrence of packet losses up to a presenttime, performs weighted averaging of the predetermined number ofdetection values by using weighting factors to provide an average numberof detection values, and calculates an estimated available bandwidthfrom the average number of detection values by using a predeterminedcalculation formula, and immediately after the communication pathswitching, the processor transits from a normal state to a transientstate, in which the weighting factors to be used are changed toweighting factors for the transient state.
 5. The image transmissionapparatus according to claim 4, wherein, when the processor is in thetransient state, the processor performs the weighted averaging of thepredetermined number of detection values by multiplying each newdetection value by a larger weighting factor than a corresponding oneused in the normal state, and multiplying each old detection value by asmaller weighting factor than a corresponding one used in the normalstate.
 6. The image transmission apparatus according to claim 4, whereinthe processor returns to the normal state when a predetermined time haselapsed after the transition to the transient state.
 7. The imagetransmission apparatus according to claim 4, wherein the processorreturns to the normal state when a number of detected packet lossesexceeds a predetermined threshold.
 8. The image transmission apparatusaccording to claim 4, wherein the processor returns to the normal statewhen a number of packets successively received after one occurrence of apacket loss exceeds a value assumed from the estimated availablebandwidth.
 9. The image transmission apparatus according to claim 4,wherein the processor returns to the normal state when a predeterminedtime has elapsed after one occurrence of a packet loss.
 10. The imagetransmission apparatus according to claim 1, wherein, when estimating anestimated available bandwidth based on an amount of occurrence of packetlosses, the processor determines whether or not each packet loss is arandom packet loss caused by external noise in the wireless section, andwhen the packet loss is determined to be a random packet loss, theprocessor eliminates the packet loss in estimation of the estimatedavailable bandwidth.
 11. An image transmission system for transmittingan image data from an image transmission apparatus to an image receptionapparatus via a communication path including a wireless section, whereinthe image transmission apparatus comprises: a communication deviceconfigured to transmit the image data to the image reception apparatus;a storage configured to store historical communication state informationwhich is information on a past communication state; and a processorconfigured to estimate a current available bandwidth based on thehistorical communication state information to control a code amount usedin encoding an image; wherein, upon occurrence of communication pathswitching, the processor acquires a temporary available bandwidth valuecorresponding to a new communication path, generates new communicationstate information corresponding to a new communication state includingat least one of packet loss rates and packet loss periods based on thetemporary available bandwidth value, replaces the historicalcommunication state information stored in the storage with the newcommunication state information, and estimates a new available bandwidthbased on the new communication state information stored in the storage.12. A code amount control method for controlling a code amount used inencoding an image to generate an image data and transmitting the imagedata to an image reception apparatus via a communication path includinga wireless section, the method comprising: estimating, by a processor, acurrent available bandwidth based on historical communication stateinformation which is information on a past communication state stored ina storage and controlling the code amount used in encoding the image;and upon occurrence of communication path switching, performing via theprocessor acquiring a temporary available bandwidth value correspondingto a new communication path, generating new communication stateinformation corresponding to a new communication state including atleast one of packet loss rates and packet loss periods based on thetemporary available bandwidth value, replacing the historicalcommunication state information stored in the storage with the newcommunication state information, and estimating a new availablebandwidth based on the new communication state information stored in thestorage.